Force Balance Design For Educational Wind Tunnels

A novel method for simulating the relative motions of the wheels and moving ground for road vehicle aerodynamics is presented. The method revisits an old concept where two identical vehicles are used and positioned so that they are mirror images, with the ground being represented by the horizontal plane of symmetry. The method involves double symmetry, where two half models (e.g. a car split down the vertical centerline) contact at the rotating wheel contact patches and the resulting (opened) vehicle halves lie on a reflection plane. This can either be the tunnel floor or the equivalent CFD plane. For some forms of physical testing this offers advantages (such as easy access to wheel cavities and requiring only one vehicle) but sealing the gap between the tunnel floor and the vehicle halves can interfere with the force balance accuracy and problems can arise with time-varying flows crossing the time averaged zero flow boundary. This paper describes the concept and CFD and model-scale EFD evaluations which were found to compare well.

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Estimation of Aerodynamic Coefficients in a Small Subsonic Wind Tunnel

PROMET - Traffic&Transportation ◽

10.7307/ptt.v30i4.2685 ◽

2018 ◽

Vol 30 (4) ◽

pp. 457-463

Author(s):

Karolina Krajček Nikolić ◽

Anita Domitrović ◽

Slobodan Janković

Keyword(s):

Reynolds Number ◽

Wind Tunnel ◽

Internal Force ◽

Force Balance ◽

Wind Tunnels ◽

Subsonic Wind Tunnel ◽

Lower Reynolds Number ◽

Scaling Methods ◽

Reynolds Number Effects ◽

Wind Tunnel Data

To apply the experimental data measured in a wind tunnel for a scaled aircraft to a free-flying model, conditions of dynamical similarity must be met or scaling procedures introduced. The scaling methods should correct the wind tunnel data regarding model support, wall interference, and lower Reynolds number. To include the necessary corrections, the current scaling techniques use computational fluid dynamics (CFD) in combination with measurements in cryogenic wind tunnels. There are a few methods that enable preliminary calculations of typical corrections considering specific measurement conditions and volume limitation of test section. The purpose of this paper is to present one possible approach to estimating corrections due to sting interference and difference in Reynolds number between the real airplane in cruise regime and its 1:100 model in the small wind tunnel AT-1. The analysis gives results for correction of axial and normal force coefficients. The results of this analysis indicate that the Reynolds number effects and the problem of installation of internal force balance are quite large. Therefore, the wind tunnel AT-1 has limited usage for aerodynamic coefficient determination of transport airplanes, like Dash 8 Q400 analyzed in this paper.

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Thermal effects influencing measurements in a supersonic blowdown wind tunnel

Thermal Science ◽

10.2298/tsci160404175v ◽

2016 ◽

Vol 20 (6) ◽

pp. 2101-2112 ◽

Cited By ~ 1

Author(s):

Djordje Vukovic ◽

Dijana Damljanovic

Keyword(s):

Wind Tunnel ◽

Thermal Effects ◽

Temperature Drop ◽

Reynolds Numbers ◽

Force Balance ◽

Wind Tunnels ◽

Large Temperature ◽

Long Run ◽

Short Run ◽

Mach And Reynolds Numbers

During a supersonic run of a blowdown wind tunnel, temperature of air in the test section drops which can affect planned measurements. Adverse thermal effects include variations of the Mach and Reynolds numbers, variation of airspeed, condensation of moisture on the model, change of characteristics of the instrumentation in the model, et cetera. Available data on thermal effects on instrumentation are pertaining primarily to long-run-duration wind tunnel facilities. In order to characterize such influences on instrumentation in the models, in short-run-duration blowdown wind tunnels, temperature measurements were made in the wing-panel-balance and main-balance spaces of two wind tunnel models tested in the T-38 wind tunnel. The measurements showed that model-interior temperature in a run increased at the beginning of the run, followed by a slower drop and, at the end of the run, by a large temperature drop. Panel-force balance was affected much more than the main balance. Ways of reducing the unwelcome thermal effects by instrumentation design and test planning are discussed.

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